CONICET | Buscador de Institutos y Recursos Humanos

Vanadium-containing molecular sieves (V-M(x)) were synthetized and applied as heterogeneous cata-lysts for the liquid phase oxidation of a-pinene with hydrogen peroxide at 70◦C. It has been found thatthe vanadium content in V-M(x) materials affected the conversion of a-pinene and product distribution.The turnover numbers increased strongly with the decreasing of V content probably caused by a high Vdispersion. The major products were verbenone, trans-sobrerol and campholenic aldehyde. The acid?baseproperties of V-M(x) affected the distribution of products formed via the isomerization of -pinene oxideover Lewis acid sites to campholenic aldehyde while Brønsted acid sites brought about the formationof 1,2 pinanediol and trans-sobrerol by hydrolysis and by the opening of oxirane ring. The increase inV content in V-M(x) led to the increase in campholenic aldehyde, 1,2 pinanediol, trans- sobrerol andover oxidation products. Moreover, the effect of several solvents on the reaction oxidation was studied.The results showed that the highest a-pinene conversions are obtained in the following order: acetoni-trile > ethanol > isoamyl alcohol > methyl ethyl ketone. Thus, using aprotic solvents, the catalytic activitywas increased and the formation of alkyl glycol ethers as by-product was not observed.The catalysts were characterized by ICP-OES, N2 adsorption,UV-Vis-DR, FT-IR, Raman and FT-IR with pyridine adsorption. Theresults confirmed that the V-M(x) samples possessed regular andstable structure with a high specific surface. The V atoms weresuccessfully introduced mainly as tetrahedral coordinated isolatedspecies into the MCM-41 framework, which would be located eitherinside the wall or on the surface of the mesoporous cannel.Leaching experiments demonstrated that very small amountsof V species were leached from the solid matrix only during thefirst and second catalytic cycle as not active species. Acetonitrileand H2O2 were involved in the lixiviation reaction forming inac-tive soluble V species, while the isolated V+ cations were stableactive sites for the oxidation of a-pinene. In addition, the catalystalso showed stability in its structure. Finally, the recycling experi-ments showed that the most active catalyst can be used repeatedlywithout activity and selectivity loss during several cycles.